Electrical conductivity measurements using microfabricated interdigitated electrodes

Microfabricated interdigitated electrode arrays were constructed and evaluated for use as miniature conductivity cells. The arrays were 2×3 mm in size and had digits ranging in size from 10 to 80 μm. The complex electrical impedance of the devices was measured at frequencies spanning from 100 to 100 kHz in solutions with resistivities ranging from 10 to 67 000 Ω/cm. An electromagnetic field model of the interdigitated electrode geometry was used to calculate cell constants. The resulting values ranged from 0.07 to 0.55 cm -1 , and they agreed well with the experimental data. The frequency dependence of the complex electrical impedance could be represented by an equivalent circuit incorporating an interfacial impedance consisting of a double-layer capacitance in series with a Warburg-type diffusion impedance